CN115637032A - Heat-resistant flame-retardant polylactic acid material and preparation method thereof - Google Patents
Heat-resistant flame-retardant polylactic acid material and preparation method thereof Download PDFInfo
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- CN115637032A CN115637032A CN202110821378.8A CN202110821378A CN115637032A CN 115637032 A CN115637032 A CN 115637032A CN 202110821378 A CN202110821378 A CN 202110821378A CN 115637032 A CN115637032 A CN 115637032A
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Abstract
The invention provides a heat-resistant flame-retardant polylactic acid material and a preparation method thereof, the heat-resistant flame-retardant polylactic acid material is prepared by blending polylactic acid and an organic hypophosphite flame retardant, the polylactic acid is selected from one or more of L-polylactic acid and D-polylactic acid, the heat-resistant flame-retardant polylactic acid material has good flame retardant property, the char formation effect, the heat resistance and the anti-dripping property of the polylactic acid material are further improved by adding the organic hypophosphite flame retardant, and the preparation method of the polylactic acid material is simple, low in cost, suitable for large-scale industrial production and further expands the application of the polylactic acid material.
Description
Technical Field
The invention belongs to the technical field of polylactic acid materials, and particularly relates to a heat-resistant flame-retardant polylactic acid material and a preparation method thereof.
Background
Polylactic acid (PLA), also known as polylactide, is a polyester made by polymerizing lactic acid as a raw material. Polylactic acid is a nontoxic and non-irritant synthetic polymer material, the raw material lactic acid is mainly obtained from fermentation of starch and the like, cellulose, kitchen waste or fish waste can also be used as raw materials, the PLA raw material has wide sources, and a product prepared from the PLA raw material can be directly composted or incinerated after being used, can be completely degraded into carbon dioxide and water, and meets the requirements of sustainable development. PLA has good transparency, certain toughness, biocompatibility, heat resistance and other properties, and has excellent biodegradability, compatibility and absorbability. In addition, PLA has thermoplasticity, can be applied to various fields, products prepared from the PLA, such as packaging materials, fibers and the like, and are mainly used in the fields of disposable articles, such as disposable tableware and packaging materials, automobile doors, foot pads, saddles, clothing, electric appliances, medical health (orthopedic internal fixation materials, non-dismantling surgical sutures and the like), and the like.
However, polylactic acid is a flammable material, the limiting oxygen index of which is about 20%, and polylactic acid has poor heat resistance and low use temperature. With the increasingly wide application of polylactic acid in the industries of electronics, automobiles and the like, people have higher and higher requirements on safety and use temperature, so how to improve the heat resistance and the flame retardant property of the polylactic acid becomes a problem to be solved urgently at present.
Disclosure of Invention
Based on the above technical background, the present inventors have made a keen search and, as a result, have found that: the mixture of L-polylactic acid and D-polylactic acid is adopted, and the organic hypophosphite flame retardant is added for blending, so that the polylactic acid material with good flame retardant property can be prepared, particularly, the addition of the flame retardant has good carbon promoting effect, the heat deformation temperature and the Vicat softening temperature of the polylactic acid material can be greatly improved, the polylactic acid material is endowed with excellent heat resistance, and meanwhile, the anti-dripping property of the polylactic acid material is improved, so that the invention is completed.
The first aspect of the invention provides a heat-resistant flame-retardant polylactic acid material, which is prepared by blending polylactic acid and an organic hypophosphite flame retardant;
the polylactic acid is selected from one or two of L-polylactic acid and D-polylactic acid.
In a second aspect of the present invention, there is provided a method for preparing the heat-resistant flame-retardant polylactic acid according to the first aspect of the present invention, the method comprising the steps of:
and 2, placing the materials dried in the step 1 into an internal mixer for blending.
The heat-resistant flame-retardant polylactic acid material and the preparation method thereof provided by the invention have the following advantages:
(1) The heat-resistant flame-retardant polylactic acid material has good flame retardant property, heat resistance and anti-dripping property;
(2) The preparation method of the heat-resistant flame-retardant polylactic acid material is simple and is suitable for industrial large-scale production.
Drawings
FIG. 1 shows temperature-lowering DSC curves of heat-resistant and flame-retardant polylactic acid materials prepared in examples 1 to 4 of the present invention and comparative examples 1 to 2;
FIG. 2 shows temperature rising DSC curves of heat-resistant and flame-retardant polylactic acid materials prepared in examples 1 to 4 of the present invention and comparative examples 1 to 2;
FIG. 3a shows TG curves of heat-resistant flame-retardant polylactic acid materials prepared in examples 1 to 4 of the present invention and comparative examples 1 to 2;
FIG. 3b is an enlarged view of the black box portion of FIG. 3 a;
FIG. 4a shows DTG curves of heat-resistant and flame-retardant polylactic acid materials prepared in examples 1 to 4 of the present invention and comparative examples 1 to 2;
FIG. 4b is an enlarged view of the black box portion of FIG. 4 a;
FIG. 5 is a photograph showing heat-resistant and flame-retardant polylactic acid materials obtained in examples 1 to 4 according to the present invention and comparative examples 1 to 2 after a vertical burning test;
FIG. 6 shows heat release curves of examples 1 to 4 and comparative examples 1 to 2;
FIG. 7 shows the total heat release curves of examples 1 to 4 and comparative examples 1 to 2;
figure 8 shows the total smoke release for examples 1 to 4 and comparative examples 1 to 2;
FIG. 9 shows photographs of carbon residues generated after burning in examples 1 to 4 and comparative examples 1 to 2;
FIG. 10 shows histograms of heat distortion temperatures for samples prepared in example 3, examples 6 to 7, comparative example 1 and comparative example 2;
FIG. 11 shows a bar graph of the Vicat softening temperatures of samples prepared in example 3, examples 6 to 7, comparative example 1 and comparative example 2;
FIG. 12 shows temperature deformation curves of samples prepared in example 3, examples 6 to 7, comparative example 1 and comparative example 2;
FIG. 13 shows the magnified temperature deformation curves of samples from 150 to 220 ℃ obtained in example 3, examples 6 to 7, comparative example 1 and comparative example 2;
FIG. 14 shows temperature-decreasing DSC curves of heat-resistant and flame-retardant polylactic acid materials obtained in examples 3 and 5 to 7 of the present invention and comparative examples 1 to 2;
FIG. 15 shows temperature-rising DSC curves of heat-resistant flame-retardant polylactic acid materials obtained in example 3, examples 5 to 7 and comparative examples 1 to 2 of the present invention;
FIG. 16 shows LOI curves of heat-resistant and flame-retardant polylactic acid materials obtained in example 3, examples 5 to 7 and comparative examples 1 to 2 of the present invention;
FIG. 17 is a photograph showing heat-resistant and flame-retardant polylactic acid materials obtained in example 3, examples 5 to 7 and comparative examples 1 to 2 according to the present invention after a vertical burning test;
FIG. 18 shows heat release rate curves of example 3, examples 6 to 7 and comparative examples 1 to 2 of the present invention;
FIG. 19 shows the total heat release amount curves of example 3, examples 6 to 7 and comparative examples 1 to 2 of the present invention;
FIG. 20 is a top view photograph showing the formation of carbon residue after combustion in examples 6 and 7 of the present invention;
FIG. 21 is a side view showing the formation of carbon residue after combustion in examples 6 and 7 of the present invention.
Detailed Description
The present invention will be described in detail below, and features and advantages of the present invention will become more apparent and apparent with reference to the following description.
The first aspect of the invention provides a heat-resistant flame-retardant polylactic acid material, which is prepared by blending polylactic acid and an organic hypophosphite flame retardant.
According to a preferred embodiment of the present invention, the polylactic acid is selected from one or two of L-polylactic acid and D-polylactic acid, preferably a mixture of L-polylactic acid and D-polylactic acid.
According to a further preferred embodiment of the present invention, the mass ratio of the L-polylactic acid and the D-polylactic acid is (0.1 to 5): 1, preferably (0.5 to 2): 1, more preferably 1:1.
The polylactic acid belongs to a non-flame-retardant material, particularly the limit oxygen index of the L-polylactic acid is extremely low, and tests show that the limit oxygen index can be improved by adding the D-polylactic acid into the L-polylactic acid, and the heat resistance of the polylactic acid material can be greatly improved.
The organic hypophosphite flame retardant is selected from one or more of organic hypophosphite halogen-free flame retardants, preferably from one or more of diethyl aluminum hypophosphite, diethyl zinc hypophosphite (ZDP), ammonium polyphosphate (APP), [ (6-oxo-6H-dibenzo- (c, e) (1,2) -oxaphosphorin-6-one) -methyl ] -succinic acid (DDP) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and more preferably from one or more of diethyl zinc hypophosphite and diethyl aluminum hypophosphite.
The inventor finds that the heat distortion temperature and the Vicat softening temperature of the polylactic acid can be further improved by adding the organic hypophosphite flame retardant into the polylactic acid, the heat resistance and the use temperature of the polylactic acid material are greatly improved, the flame retardant property of the polylactic acid material can be improved, and the polylactic acid material has a good application prospect.
In the present invention, the mass ratio of the organic hypophosphite flame retardant to the polylactic acid is (0.01 to 0.5): 1, preferably (0.03 to 0.4): 1, and more preferably (0.05 to 0.25): 1.
The ultimate oxygen index and the anti-dripping performance of the polylactic acid material can be further improved by adding the organic hypophosphite flame retardant into the polylactic acid material, the carbon residue rate of the polylactic acid material is increased along with the increase of the organic hypophosphite flame retardant, good high-temperature char formation is very favorable for flame-retardant modification of polymers, the ultimate oxygen index and the heat distortion temperature of the polylactic acid material are also gradually improved along with the increase of the organic hypophosphite flame retardant, but along with the further increase of the organic hypophosphite flame retardant, if the mass ratio of the organic hypophosphite flame retardant to the polylactic acid is more than 0.25:1, the heat distortion temperature is reduced.
The heat-resistant flame-retardant polylactic acid material has the limiting oxygen index of 22-27%, the thermal deformation temperature of 160-180 ℃, the Vicat softening temperature of 145-170 ℃ and excellent anti-dripping performance.
In a second aspect of the present invention, there is provided a method for preparing the heat-resistant flame-retardant polylactic acid material according to the first aspect of the present invention, the method comprising the steps of:
and 2, placing the materials dried in the step 1 into an internal mixer for blending.
This step is specifically described and illustrated below.
The polylactic acid is selected from one or two of L-polylactic acid and D-polylactic acid, and is preferably a mixture of the L-polylactic acid and the D-polylactic acid.
The mass ratio of the L-polylactic acid to the D-polylactic acid is (0.1-5): 1, preferably (0.5-2): 1, and more preferably 1:1.
The organic hypophosphite flame retardant is selected from one or more of organic hypophosphite halogen-free flame retardants, preferably from one or more of diethyl aluminum hypophosphite, diethyl zinc hypophosphite (ZDP), ammonium polyphosphate (APP), [ (6-oxo-6H-dibenzo- (c, e) (1,2) -oxaphosphorin-6-one) -methyl ] -succinic acid (DDP) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)), and more preferably from one or more of diethyl zinc hypophosphite and diethyl aluminum hypophosphite.
The mass ratio of the organic hypophosphite flame retardant to the polylactic acid is (0.01-0.5): 1, preferably (0.03-0.4): 1, and more preferably (0.05-0.25): 1.
The addition of the organic hypophosphite can improve the limited oxygen index of the polylactic acid material, improve the flame retardant property of the polylactic acid material, and is particularly beneficial to improving the service temperature and the anti-dripping property of the polylactic acid material, and the higher the service temperature of the polylactic acid material is, the better the dimensional stability is when the polylactic acid material is heated, and the smaller the thermal deformation is. The better the flame retardant property and the anti-dripping property, the more difficult the material is to ignite, spread and cause scald in fire, and the application prospect of the polylactic acid material can be effectively improved by adding the organic hypophosphite into the polylactic acid material.
The drying is carried out in a vacuum oven, and the drying temperature is 40-80 ℃, preferably 50-70 ℃, and more preferably 60 ℃.
The drying time is 10 to 20 hours, preferably 11 to 15 hours, and more preferably 12 hours.
The drying is carried out before blending to remove the crystal water in the polylactic acid, weaken the degradation of the polylactic acid in the blending process and be beneficial to improving the performance of the prepared heat-resistant flame-retardant polylactic acid material.
And 2, placing the materials dried in the step 1 into an internal mixer for blending.
The blending temperature is 160 to 220 ℃, preferably 170 to 210 ℃, and more preferably 180 to 200 ℃.
The blending is carried out under the melting state, the blending under the melting state is beneficial to more uniform mixing of materials, and the blending under the high temperature is beneficial to improving the content of SC-crystals.
The blending time is 2 to 10min, preferably 3 to 7min, and more preferably 4 to 6min.
The blending time is short, the compatibility and uniformity of the blended polylactic acid and the flame retardant are poor, the flame retardant effect of the flame retardant on the polylactic acid is poor, and if the mixing time is too long, the degradation of the polylactic acid material can be caused, and the heat resistance, flame retardance, mechanics and other properties of the material can be influenced. The rotational speed of the internal mixer is 30 to 100rpm, preferably 40 to 80rpm, and more preferably 50 to 70rpm.
The compatibility and uniformity of the polylactic acid and the flame retardant can influence the improvement of the flame retardant property of the flame retardant to the polylactic acid, the compatibility is closely related to the processing technology, and the adoption of a larger rotating speed is favorable for improving the compatibility in the melting and mixing process of the polylactic acid and the flame retardant, so that the flame retardant effect is further improved.
After blending, isothermal treatment is carried out, the temperature is 160-180 ℃, preferably 170 ℃, and the isothermal time is 1-5 min, preferably 1-2 min.
The isothermal treatment can remove the bound water in the heat-resistant and flame-retardant polylactic acid material, and is convenient for later injection molding and the like.
The third aspect of the invention provides an anti-molten-drop heat-resistant flame-retardant polylactic acid material, which is prepared by blending raw materials comprising polylactic acid and a melamine-based flame retardant.
The polylactic acid is selected from one or two of L-polylactic acid and D-polylactic acid, and is preferably a mixture of the L-polylactic acid and the D-polylactic acid.
The L-polylactic acid has a low limit oxygen index and is a non-flame-retardant material, and the inventor finds that the addition of the D-polylactic acid in the L-polylactic acid can not only improve the limit oxygen index of the polylactic acid material, but also improve the heat resistance of the polylactic acid material.
In a preferred embodiment of the present invention, the mass ratio of L-polylactic acid to D-polylactic acid is (0.1 to 5): 1, the mass ratio is preferably (0.5 to 2): 1, and more preferably 1:1.
In the invention, the melamine-based flame retardant is selected from one or more of melamine phthalate, melamine phytate, melamine cyanurate and melamine tristhiocyanate, preferably selected from one or two of melamine phthalate and melamine cyanurate, and more preferably selected from melamine cyanurate.
Through a large number of experiments, the inventor finds that the heat resistance and the flame retardance of the polylactic acid can be improved by adding the melamine-based flame retardant into the polylactic acid.
The mass ratio of the melamine-based flame retardant to the polylactic acid is (0.02-0.5): 1, preferably (0.04-0.3): 1, and more preferably (0.05-0.25): 1.
According to a preferred embodiment of the present invention, the raw material further comprises an organic hypophosphite flame retardant.
Tests show that the ultimate oxygen index, the molten drop resistance and the heat resistance of the polylactic acid material can be greatly improved by further adding the organic hypophosphite flame retardant into the polylactic acid material, the organic hypophosphite flame retardant and the melamine flame retardant are added together to achieve a synergistic effect, and the effect of improving the flame retardance and the heat resistance of the polylactic acid material is more obvious than that of independently adding the organic hypophosphite or melamine flame retardant.
The organic hypophosphite flame retardant is selected from one or more of organic hypophosphite halogen-free flame retardants, preferably from one or more of diethyl aluminum hypophosphite (ADP), diethyl zinc hypophosphite (ZDP), ammonium polyphosphate (APP), [ (6-oxo-6H-dibenzo- (c, e) (1,2) -oxaphosphorin-6-one) -methyl ] -succinic acid (DDP) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)), and more preferably from one or more of diethyl zinc hypophosphite and diethyl aluminum hypophosphite.
The inventor finds that the combined action of the organic hypophosphite halogen-free flame retardant and the melamine flame retardant has a more obvious effect on improving the polylactic acid, the heat resistance of the polylactic acid can be greatly improved, the limiting oxygen index and the molten drop resistance of the polylactic acid can be greatly improved, meanwhile, the melamine flame retardant and the organic hypophosphite can also have a carbon promoting effect by being added simultaneously, an expansion layer is formed on the surface of the polylactic acid after combustion, the total heat release amount is reduced, the combustion time is greatly shortened, and excellent flame retardance is shown.
The mass ratio of the melamine-based flame retardant to the organic hypophosphite is (0.5-5) to 1, and preferably (0.7-4): 1, more preferably in a mass ratio of (0.8 to 3): 1.
the mass ratio of the melamine-based flame retardant to the organic hypophosphite can influence the synergistic effect of the two flame retardants, and further influence the improvement effect of the melamine-based flame retardant to the heat resistance and the flame retardancy of the polylactic acid material.
The limiting oxygen index of the anti-molten drop heat-resistant flame-retardant polylactic acid material is 23-33%, the thermal deformation temperature is 170-210 ℃, the Vicat softening temperature is 160-200 ℃, and the UL-94 vertical combustion grade reaches V-0 grade.
The fourth aspect of the present invention provides a preparation method of the anti-dripping, heat-resistant and flame-retardant polylactic acid material according to the third aspect of the present invention, the preparation method comprises: and (3) putting the dried raw materials into an internal mixer for blending.
In the present invention, the raw materials include polylactic acid and melamine-based flame retardant
The polylactic acid is selected from one or two of L-polylactic acid and D-polylactic acid, and is preferably a mixture of the L-polylactic acid and the D-polylactic acid.
The mass ratio of the L-polylactic acid to the D-polylactic acid is (0.1-5): 1, preferably the mass ratio of (0.5-2): 1, more preferably 1:1.
The melamine-based flame retardant is selected from one or more of melamine phthalate, melamine phytate, melamine cyanurate and melamine tristhiocyanate, preferably selected from one or two of melamine phthalate and melamine cyanurate, and more preferably selected from melamine cyanurate.
The mass ratio of the melamine-based flame retardant to the polylactic acid is (0.02-0.5): 1, preferably (0.04-0.3): 1, more preferably (0.05-0.25): 1.
according to a preferred embodiment of the present invention, the raw material further comprises an organic hypophosphite flame retardant.
The organic hypophosphite flame retardant is selected from one or more of organic hypophosphite halogen-free flame retardants, preferably from one or more of diethyl aluminum hypophosphite (ADP), diethyl zinc hypophosphite (ZDP), ammonium polyphosphate (APP), [ (6-oxo-6H-dibenzo- (c, e) (1,2) -oxaphosphorin-6-one) -methyl ] -succinic acid (DDP) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)), and more preferably from one or more of diethyl zinc hypophosphite and diethyl aluminum hypophosphite.
The mass ratio of the melamine flame retardant to the organic hypophosphite flame retardant is (0.5-5): 1, preferably the mass ratio is (0.7-4): 1, more preferably in a mass ratio of (0.8 to 3): 1.
the drying is carried out in a vacuum oven, and the drying temperature is 60-120 ℃, preferably 80-110 ℃, and more preferably 100 ℃.
The drying before blending can remove the crystal water in the polylactic acid, weaken the degradation of the polylactic acid in the blending process and be beneficial to improving the heat resistance and the flame retardance of the heat-resistant flame-retardant polylactic acid material.
The drying time is 5 to 20 hours, preferably 10 to 15 hours, and more preferably 12 hours.
The blending temperature is 160 to 220 ℃, preferably 170 to 210 ℃, and more preferably 180 to 200 ℃.
The blending is carried out within the temperature range, so that the polylactic acid material is in a molten state during blending, the material mixing is more uniform, the content of SC crystals is increased, and the heat resistance and the flame retardance of the polylactic acid material are increased as the content of SC stereo crystals is increased.
The blending time is 2 to 10min, preferably 3 to 7min, and more preferably 4 to 6min.
The blending time can influence the mixing uniformity of the polylactic acid and the flame retardant, and further influence the improvement effect of the flame retardant on the flame retardance and the heat resistance of the polylactic acid, but the blending time is too long, the polylactic acid material can be degraded, and tests show that when the blending time is within the range, the polylactic acid can not be degraded, and the flame retardant has a good improvement effect on the heat resistance and the flame retardance of the polylactic acid.
The rotational speed of the internal mixer is 30 to 100rpm, preferably 40 to 80rpm, and more preferably 50 to 70rpm.
The blending is stirred under high-speed stirring, and if the stirring speed is too low, the mixing uniformity is low, which is not favorable for the improvement effect of the flame retardant on the polylactic acid.
And after the blending is finished, carrying out isothermal treatment, wherein the isothermal treatment temperature is 160-180 ℃, preferably 170 ℃, and the isothermal treatment time is 1-5 min, preferably 1-2 min.
After blending, isothermal treatment is carried out, so that bound water in the anti-molten drop heat-resistant flame-retardant polylactic acid material can be further removed, and later-stage use is facilitated.
The invention has the following beneficial effects:
(1) The heat-resistant flame-retardant polylactic acid material has good flame-retardant property, and the limiting oxygen index of the material is more than 22%;
(2) The heat-resistant flame-retardant polylactic acid material has the heat deformation temperature of 170.4 ℃, the Vicat softening temperature of 165 ℃, good dimensional stability when heated, small heat deformation, excellent heat resistance and good application prospect;
(3) The heat-resistant flame-retardant polylactic acid material disclosed by the invention is excellent in molten drop resistance, obvious in carbon forming effect during heating combustion, and capable of keeping the shape of a sample for a long time;
(4) The limiting oxygen index of the anti-molten drop heat-resistant flame-retardant polylactic acid material can reach 33%, the thermal deformation temperature can reach 209.8 ℃, the Vicat softening temperature can reach 189.9 ℃, the anti-molten drop performance is excellent, and the UL-94 vertical combustion grade reaches V-0 grade;
(5) The polylactic acid material prepared by the method has wide raw material sources, can be prepared by simple one-step blending, has low preparation cost, and is suitable for large-scale industrial production.
Examples
The invention is further illustrated by the following specific examples, which are intended to be illustrative only and not limiting to the scope of the invention.
Example 1
Putting L-polylactic acid (REVODE 190) (PLLA), D-polylactic acid (TOTAL, D120) (PDLA) and diethyl aluminum hypophosphite (ADP) into a vacuum oven for vacuum drying for 12 hours at the drying temperature of 60 ℃, uniformly mixing the PLLA and the PDLA with the ADP accounting for 5 percent of the TOTAL mass of the polylactic acid according to the proportion of 1:1, adding the mixture into an internal mixer for blending, wherein the blending temperature is 190 ℃, the rotating speed is 60rpm/min, the blending time is 5min, and carrying out isothermal treatment at 170 ℃ for 2min after blending is finished, thereby finally preparing the PLLA/PDLA/ADP5 heat-resistant flame-retardant polylactic acid material.
Example 2
The preparation of a heat resistant flame retardant polylactic acid material was carried out in a similar manner to example 1, except that: uniformly mixing PLLA and PDLA with the proportion of 1:1 and ADP accounting for 10% of the total mass of polylactic acid, adding the mixture into an internal mixer for blending, and finally preparing the heat-resistant and flame-retardant polylactic acid material PLLA/PDLA/ADP 10.
Example 3
The preparation of a heat resistant flame retardant polylactic acid material was carried out in a similar manner to example 1, except that: uniformly mixing PLLA and PDLA with ADP accounting for 15% of the total mass of polylactic acid according to the proportion of 1:1, adding the mixture into an internal mixer for blending, and finally preparing the PLLA/PDLA/ADP15 heat-resistant flame-retardant polylactic acid material.
Example 4
The preparation of a heat and flame resistant polylactic acid material was carried out in a similar manner to example 1, except that: uniformly mixing PLLA and PDLA with the proportion of 1:1 and ADP accounting for 20% of the total mass of polylactic acid, adding the mixture into an internal mixer for blending, and finally preparing the heat-resistant and flame-retardant polylactic acid material PLLA/PDLA/ADP 20.
Example 5
Putting L-polylactic acid (REVODE 190) (PLLA), D-polylactic acid (TOTAL 120) (PDLA) and Melamine Cyanurate (MCA) into a vacuum oven for vacuum drying for 12h, wherein the drying temperature is 100 ℃, uniformly mixing the PLLA and the PDLA with the MCA accounting for 15 percent of the TOTAL mass of the polylactic acid according to the proportion of 1:1, adding the mixture into an internal mixer for blending, the blending temperature is 190 ℃, the rotating speed is 60rpm/min, the blending time is 5min, and after the blending is finished, carrying out isothermal treatment at 170 ℃ for 2min to finally prepare the PLLA/PDLA/MCA15 heat-resistant flame-retardant polylactic acid material.
Example 6
Putting L-polylactic acid (REVODE 190) (PLLA), D-polylactic acid (TOTAL, D120) (PDLA), diethyl aluminum hypophosphite (ADP) and Melamine Cyanurate (MCA) into a vacuum oven for vacuum drying for 12 hours at the drying temperature of 100 ℃, uniformly mixing the PLLA and the PDLA with MCA accounting for 15 percent of the TOTAL mass of the polylactic acid and ADP accounting for 15 percent of the TOTAL mass of the polylactic acid according to the proportion of 1:1, adding the mixture into an internal mixer for blending, wherein the blending temperature is 190 ℃, the rotating speed is 60rpm/min, the blending time is 5min, and carrying out isothermal treatment at 170 ℃ for 2min after blending is finished, thereby finally preparing the PLLA/PDLA/MCA15/ADP15 heat-resistant flame-retardant polylactic acid material.
Example 7
Putting L-polylactic acid (REVODE 190) (PLLA), D-polylactic acid (TOTAL, D120) (PDLA), diethyl aluminum hypophosphite (ADP) and Melamine Cyanurate (MCA) into a vacuum oven for vacuum drying for 12 hours at the drying temperature of 100 ℃, uniformly mixing the PLLA and the PDLA with MCA accounting for 20 percent of the TOTAL mass of the polylactic acid and ADP accounting for 10 percent of the TOTAL mass of the polylactic acid according to the proportion of 1:1, adding the mixture into an internal mixer for blending, wherein the blending temperature is 190 ℃, the rotating speed is 60rpm/min, the blending time is 5min, and carrying out isothermal treatment at 170 ℃ for 2min after blending is finished, thereby finally preparing the PLLA/PDLA/MCA20/ADP10 heat-resistant flame-retardant polylactic acid material.
Comparative example
Comparative example 1
Putting L-polylactic acid (REVODE 190) (PLLA) into a vacuum oven for vacuum drying for 24h, wherein the drying temperature is 80 ℃, adding the PLLA into an internal mixer for blending, the blending temperature is 190 ℃, the rotating speed is 60rpm/min, and the blending time is 5min, so as to obtain the PLLA polylactic acid material.
Comparative example 2
Putting L-polylactic acid (REVODE 190) (PLLA) and D-polylactic acid (TOTAL 120) (PDLA) into a vacuum oven for vacuum drying for 24 hours at the drying temperature of 80 ℃, uniformly mixing the PLLA and the PDLA in the proportion of 1:1, adding the mixture into an internal mixer for blending, wherein the blending temperature is 190 ℃, the rotating speed is 60rpm/min, and the blending time is 5min, and finally preparing the PLLA/PDLA polylactic acid material.
Examples of the experiments
Experimental example 1DSC test
Examples 1-7 and comparative examples 1-2 were tested using a TA differential scanning calorimeter (DSC Q2000, TA Instruments) of the United states corporation, and the samples had a mass of about 5-9 mg. Under the protection of nitrogen atmosphere, the temperature of the sample is raised to 250 ℃ at the speed of 30 ℃/min, the temperature is maintained for 5min, the temperature is lowered to 30 ℃ at the cooling rate of 10 ℃/min, the temperature is raised to 250 ℃ at the heating rate of 10 ℃/min, and the temperature lowering curve and the second heating curve of the sample are recorded. The test results of examples 1 to 4 and comparative examples 1 to 2 are shown in fig. 1 and 2, respectively. The test results of example 3, examples 5 to 7 and comparative examples 1 to 2 are shown in fig. 14 and fig. 15, respectively.
As can be seen from fig. 1 and 14, the PLLA polylactic acid material obtained in comparative example 1 hardly has thermal crystallization during temperature reduction, a sharp cold crystallization peak near 105 ℃ and a sharp melting peak near 175 ℃ are shown in fig. 2 and 15 (during second temperature rise), the PLLA/PDLA polylactic acid material obtained in comparative example 2 has a small thermal crystallization peak near 105 ℃ during temperature reduction, a more gradual cold crystallization peak near 105 ℃ than that of the PLLA polylactic acid material during second temperature rise, a sharp melting peak near 175 ℃ and a more gradual melting peak near 225 ℃, which indicates that the PLLA/PDLA polylactic acid material has a small amount of SC crystal form.
The sample added with ADP has a sharp thermal crystallization peak near 175 ℃ in the process of temperature reduction, a relatively flat crystallization peak near 125 ℃, a small melting peak near 175 ℃ in the process of second temperature rise, and a large melting peak near 225 ℃, and the thermal crystallization peak at 175 ℃ in the process of temperature reduction is judged to be the crystallization peak of SC crystal form, the thermal crystallization peak near 105 ℃ is the crystallization peak of alpha crystal form, while the melting peak near 175 ℃ in the process of second temperature rise is the melting peak of alpha crystal form, and the melting peak near 225 ℃ is the melting peak of SC crystal form. It was found that the addition of PDLA can promote the formation of a small amount of SC crystal form and the addition of ADP can promote the formation of a large amount of SC crystal form. And the PLLA/PDLA/ADP10 sample has the best effect, namely the SC crystal content is the most.
As can be seen from fig. 14 and fig. 15, PLLA/PDLA/MCA15 shows a relatively flat crystallization peak of SC crystal at about 190 ℃ during the first temperature decrease, and a smaller crystallization peak at about 128 ℃, which is a crystallization peak of α crystal form, while PLLA/PDLA/MCA15 shows a small α crystal melting peak at 175 ℃ and a larger SC crystal melting peak at about 225 ℃ during the second temperature increase curve, which indicates that adding 15% MCA to polylactic acid is beneficial to SC crystal formation and accelerates the crystallization rate.
In the samples added with ADP and MCA, PLLA/PDLA/MCA15/ADP15 and PLLA/PDLA/MCA20/ADP10 respectively have a sharp SC crystal crystallization peak near 190 ℃ in the first temperature reduction process, and have an alpha crystal melting peak near 175 ℃ and a large SC crystal melting peak near 225 ℃ in the second temperature rise process, which shows that the ADP and MCA are simultaneously added into polylactic acid to promote the generation of SC crystals, improve the crystallization rate and inhibit the formation of alpha crystals.
Experimental example 2TG test
The samples prepared in examples 1 to 4 and comparative examples 1 to 2 and the thermal stability of ADP were tested using a thermogravimetric analyzer of Netzsch type 209F1, a company resistant to relaxation, germany. And (3) testing conditions are as follows: n is a radical of 2 The temperature range of the atmosphere is 30-700 ℃, and the heating rate is 20 ℃/min. The TG curve and DTG curve are shown in fig. 3a, fig. 3b, fig. 4a and fig. 4b, respectively, fig. 3b is an enlarged view of the black box in fig. 3a, and fig. 4b is an enlarged view of the black box in fig. 4 a.
As can be seen from FIGS. 3a, 3b, 4a and 4b, the TG curve and DTG curve of the samples prepared in comparative example 1 and comparative example 2 almost coincide, the thermal decomposition temperature is approximately around 318 ℃, the maximum thermal decomposition temperature is around 363 ℃, ADP starts to decompose at 406 ℃, when the temperature reaches 471 ℃, the thermal decomposition rate of ADP reaches the maximum, two stages occur in the sample added with ADP, the first stage lowering process is the thermal degradation process of PLLA/PDLA, and the second stage lowering process is the thermal decomposition process of ADP.
The first plateau of the PLLA/PDLA/ADP5 sample was dropped at 284 deg.C and the maximum thermal decomposition temperature was 344 deg.C, the second plateau began to drop at 406 deg.C, and the thermal decomposition rate of ADP reached a maximum when the temperature reached 430 deg.C.
The second plateau began to drop at 279 ℃ for the first plateau temperature and 337 ℃ for the maximum thermal decomposition temperature of the PLLA/PDLA/ADP10 sample, since ADP began to decompose and the rate of thermal decomposition of ADP reached a maximum when the temperature reached 431 ℃.
The first plateau temperature of the PLLA/PDLA/ADP15 sample decreased at 277 ℃ and the maximum thermal decomposition temperature was 338 ℃ and the second plateau began to decrease at 406 ℃ as well, with the maximum rate of ADP thermal decomposition reaching 451 ℃.
The first plateau of the PLLA/PDLA/ADP20 sample was lowered at 267 ℃ and the maximum thermal decomposition temperature was 338 ℃ and the second plateau was started to lower at 406 ℃ as well, and the rate of ADP thermal decomposition was maximized when the temperature reached 456 ℃.
From the above, it can be seen that the thermal decomposition of PLLA/PDLA is accelerated by adding ADP, the higher the ADP addition amount is, the lower the thermal decomposition temperature of the sample is, the maximum heat release rate of the sample has no obvious change basically, ADP starts to decompose after 406 ℃, the maximum decomposition rate of ADP in the sample gradually increases with the increase of ADP content, and the maximum thermal decomposition temperature thereof also increases.
Experimental example 3LOI test
The LOI values of the samples obtained in examples 1 to 7 and comparative examples 1 to 2 were measured with a Dynisco oxygen index tester of the United states, the sample size was 80 mm. Times.6.5 mm. Times.3 mm, and the test standards were in accordance with GB/T2406.2-2009 determination of the burning behavior of plastics by oxygen index method. The test results of examples 1 to 4 and comparative examples 1 to 2 are shown in table 1. The test results of example 3, examples 5 to 7 and comparative examples 1 to 2 are shown in FIG. 16.
TABLE 1 flame retardancy test results
| Sample name | LOI(％) |
| Comparative example 1 | 19 |
| Comparative example 2 | 21 |
| Example 1 | 22 |
| Example 2 | 22 |
| Example 3 | 26 |
| Example 4 | 27 |
As can be seen from Table 1, the limiting oxygen index of the PLLA polylactic acid in comparative example 1 is only 19%, the PLLA polylactic acid belongs to non-flame-retardant materials, the limiting oxygen index of the sample prepared in comparative example 2 is 21%, which indicates that the formation of SC (single crystal) stereo crystals is helpful for improving the limiting oxygen index of the material, but the flame-retardant effect is small, the limiting oxygen index of the prepared sample is gradually increased along with the increase of flame retardants, and when the addition amount of the flame retardants is 20%, the limiting oxygen index can reach 27%, which indicates that the flame retardant performance of the polylactic acid can be improved by adding the flame retardants of the invention.
As can be seen from FIG. 16, the limiting oxygen index of the PLLA/PDLA/MCA15 sample is 23%, the limiting oxygen index of the PLLA/PDLA/ADP15 sample can reach 26%, the limiting oxygen indexes of the samples PLLA/PDLA/MCA15/ADP15 and PLLA/PDLA/MCA20/ADP10 obtained by simultaneously adding MCA and ADP can reach 33%, the flame retardant property is greatly improved, and the flame retardant property of polylactic acid can be greatly improved by simultaneously adding MCA and ADP.
Experimental example 4 vertical Combustion Performance test
The samples prepared in examples 1 to 7 and comparative examples 1 to 2 were subjected to a vertical combustion performance test using a model CZF-3 horizontal vertical combustor, jiangning district analytical instrument factory in Nanjing, with a spline size of 130mm × 13mm × 3mm, according to GB/T2408-2008 "horizontal and vertical methods for testing Plastic Combustion Performance". The test results of examples 1 to 4 and comparative examples 1 to 2 are shown in table 2 and fig. 5. The test results of example 3, examples 5 to 7 and comparative examples 1 to 2 are shown in table 2 and fig. 17.
TABLE 2 vertical Combustion Performance test
| Sample name | Whether molten drop or not | Whether ignition of absorbent cotton | Grade |
| Comparative example 1 | Is that | Is that | V-2 |
| Comparative example 2 | Is that | Is that | V-2 |
| Example 1 | Is that | Is that | V-2 |
| Example 2 | Is that | Is that | V-2 |
| Example 3 | Whether or not | Whether or not | V-2 |
| Example 4 | Whether or not | Whether or not | V-2 |
| Example 5 | Is that | Is that | V-2 |
| Example 6 | Whether or not | Whether or not | V-0 |
| Example 7 | Whether or not | Whether or not | V-0 |
As can be seen from Table 2, the heat-resistant and flame-retardant polylactic acid prepared in examples 3 and 4 has excellent anti-dripping performance, which indicates that the anti-dripping performance of the polylactic acid material can be improved by adding the flame retardant of the invention. As can be seen from FIG. 5, the samples prepared in examples 3 and 4 can keep shapes for a long time, and the more flame retardants are added, the more carbon forming effect is obvious, and the more durable the shape of the sample can be kept.
The vertical burning test result shows that the PLLA/PDLA/ADP15 sample can temporarily keep the shape, but the burning time is long and still only V-2 grade compared with the pure PLLA sample and the PLLA/PDLA sample, and the PLLA/PDLA/MCA15/ADP15 and PLLA/PDLA/MCA20/ADP10 samples prepared after MCA and ADP are simultaneously added have no molten drop phenomenon, short burning time and quicker flame extinction, and as can be seen from FIG. 17, the sample can keep the shape permanently and show more excellent molten drop resistance and flame retardance.
Experimental example 5CONE test
Examples 1 to 7 and comparative examples 1 to 2 were tested using a Standard cone Calorimeter (FTT Standard Corn Calorimeter) from Fire Testing Technology Ltd, UK, and the heat radiation power was 35kW/m 2 The sample size is 100mm × 100mm × 3mm, and the test standard is according to ISO 5660-1 part 1 of test for heat release, smoke yield and mass loss rate of the flame reaction: heat release rate (cone calorimeter method), heat release, total heat release, and total smoke release of examples 1 to 4 and comparative examples 1 to 2 are shown in fig. 6, 7, and 8, respectively. The heat release rate and the total heat release amount of example 3, examples 6 to 7, and comparative examples 1 to 2 are shown in fig. 18 and fig. 19, respectively.
As can be seen from FIGS. 6 and 7, the addition of ADP has a certain effect on reducing HRR (heat release), and as the addition amount of ADP increases, HRR gradually decreases, and the HRR value of the sample with 20% ADP content decreases to 300KW/m 2 Left and right. The total heat release amount is effectively improved, and the THR (total heat release) value is reduced with the increase of the ADP content. PLA is a degradable material and the smoke release is small, and as can be seen from fig. 8, the TSR (total smoke release) of the sample gradually increases with the increase of the ADP content in the sample.
Carbon residue after combustion as shown in fig. 9, PLLA and PLLA/PDLA had almost no residue, while the samples after addition of ADP had different degrees of residue, indicating that ADP addition helped char formation, further illustrating the char-contributing effect of ADP on polylactic acid. Good high-temperature char formation is very beneficial to flame retardant modification of the polymer, on one hand, the flame retardant property of the polymer can be enhanced due to high char formation, and on the other hand, the high char formation is beneficial to reducing smoke release and heat release in the combustion process.
As can be seen from FIGS. 18 and 19, the difference between the heat release rate and the total heat release amount is small between pure PLLA and PLLA/PDLA, and the peak value of the heat release rate is 500KW/m 2 About, the total heat release amount is 86m 2 /m 2 On the left, the addition of ADP has a certain effect on reducing HRR and THR, and MCA and ADP are added simultaneouslyHRR peak values of PLLA/PDLA/MCA15/ADP15 and PLLA/PDLA/MCA20/ADP10 samples of the flame retardant are further reduced to 360KW/m 2 The total heat release decreased to 70m relative to the pure PLLA sample by 28% 2 /m 2 About, the flame retardant property is effectively improved in the aspect of heat release compared with that of a pure PLLA sample by 18.6 percent.
As shown in FIGS. 20 and 21, the samples after MCA and ADP addition had more residue after combustion, and as can be seen from FIG. 21, the residue after combustion of the samples of examples 6 and 7 had a peaky swollen morphology, indicating that the addition of MCA and ADP together served as a condensed phase flame retardant.
Experimental example 6 test of thermal deformation Properties
The GTS-III type thermal deformation performance measuring instrument of Shanghai Kaidi new material science and technology company Limited is adopted. The powder sample prepared in example 1 was kept at a temperature of 120 ℃ for 30min and then taken out, the powder sample prepared in comparative example 2 was kept at a temperature of 130 ℃ for 10min and then taken out, the powder samples prepared in example 3 and examples 6 to 7 were kept at a temperature of 170 ℃ for 2min and then taken out, and a small piece of the sample was cut out to be subjected to a heat distortion temperature test, wherein the thickness of the sample strip: 3-4mm, test conditions: the temperature range is from room temperature to 235 ℃, the heating rate is 10 ℃/min, and the pressure is 200Mpa. The test results of comparative examples 1 to 2, example 3 and examples 6 to 7 are shown in fig. 10.
As can be seen from FIG. 10, the HDT (heat distortion) temperature of pure PLLA is only 65.1 ℃, the HTD temperature of PLLA/PDLA samples can be increased to 156.8 ℃, while the HDT temperature of PLLA/PDLA/ADP15 samples can be as high as 170.4 ℃, which is 161.8% higher than that of pure PLLA samples, and the heat resistance is excellent, and the use temperature of polylactic acid is increased.
HDT of the PLLA/PDLA/MCA20/ADP10 sample reaches 176.9 ℃, HDT of the PLLA/PDLA/MCA15/ADP15 sample can reach 209.8 ℃, and the HDT is improved by 222.27 percent compared with that of a pure PLLA sample, so that the heat resistance is excellent.
Experimental example 7 Vicat softening temperature test
The Vicat softening temperature is the temperature at which a sample is pressed 1 mm by a1 mm square plunger under a certain load and constant temperature rise conditions with a thermoplastic placed in a liquid heat transfer medium. The microcard softening temperature is one of indexes for evaluating the heat resistance of the material and reflecting the physical and mechanical properties of the product under the heated condition. The Vicat softening temperature of a material cannot be directly used for evaluating the actual use temperature of the material, but can be used for guiding the quality control of the material. The higher the Vicat softening temperature, the better the dimensional stability of the material when heated, the lower the thermal deformation, i.e.the better the resistance to thermal deformation, the higher the rigidity and the higher the modulus.
The powder sample prepared in example 1 was kept at 120 ℃ for 30min and then taken out, the powder sample prepared in comparative example 2 was kept at 130 ℃ for 10min and then taken out, the powder samples prepared in example 3 and examples 6 to 7 were kept at 170 ℃ for 2min and then taken out, and a small piece of the sample was cut out for vicat softening temperature test. The test results of example 3, comparative examples 1 to 2 and examples 6 to 7 are shown in FIG. 11.
As can be seen in FIG. 11, the VST (Vicat softening temperature) of the pure PLLA samples was only 78.6 deg.C, the VST of the PLLA/PDLA samples increased to 163.7 deg.C, and the VST of the PLLA/PDLA/ADP15 samples reached 165 deg.C, which was an increase of 109.9%.
The VST of the PLLA/PDLA/MCA20/ADP10 sample can reach 174.3 ℃, the VST of the PLLA/PDLA/MCA15/ADP15 sample reaches 189.9 ℃, and the VST is improved by 141.6 percent compared with that of a pure PLLA sample. Exhibits excellent heat resistance.
Experimental example 8 temperature deformation test
The powder sample prepared in example 1 was kept at 120 ℃ for 30min and then taken out, the powder sample prepared in comparative example 2 was kept at 130 ℃ for 10min and then taken out, the powder samples prepared in example 3 and examples 5 to 7 were kept at 170 ℃ for 2min and then taken out, and a small section of the sample was cut out for temperature deformation curve testing. The test results of example 3, examples 5 to 7 and comparative examples 1 to 2 are shown in fig. 12 and 13, respectively.
As can be seen in fig. 12, the PLLA sample showed an inflection point at 172.13 ℃, which is when the melting point of the alpha crystals was reached, and only the alpha crystals were in the PLLA matrix. The PLLA/PDLA (comparative example 2) sample showed a small step at 63 ℃, relatively more pronounced than the other two samples, a first inflection point at 180.12 ℃ which may be the melting of a portion of the alpha and beta crystals in the matrix, and a second inflection point at 214.95 ℃ which is the melting of the SC crystals. The glass transition was hardly evident in the PLLA (comparative example 1) and PLLA/PDLA/ADP15 (example 3) samples in FIG. 13, indicating that both samples crystallized sufficiently. The PLLA/PDLA/ADP15 sample showed an inflection around 187 ℃ which is the melting of SC crystals. Therefore, the service temperature of the PLLA/PDLA/ADP15 sample is improved by 8.64 percent compared with that of the PLLA sample, and the sample has good heat deformation resistance.
The inflection points of the PLLA/PDLA/ADP15 and PLLA/PDLA/MCA15 samples are both around 187 ℃, and the inflection points of the PLLA/PDLA/MCA20/ADP10 and PLLA/PDLA/MCA15/ADP15 samples are about 220 ℃, which is improved by 27.81 percent compared with the pure PLLA sample. It is shown that the addition of PDLA and ADP, MCA to PLLA and the isothermal treatment at an appropriate temperature have a significant effect on the deformation temperature of the sample. Thus proving that the addition of ADP and MCA is effective in improving the heat resistance of the material.
The invention has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to be construed in a limiting sense. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its embodiments without departing from the spirit and scope of the present invention, which fall within the scope of the present invention. The scope of the invention is defined by the appended claims.
Claims (10)
1. A heat-resistant flame-retardant polylactic acid material is characterized in that the heat-resistant flame-retardant polylactic acid material is prepared by blending polylactic acid and an organic hypophosphite flame retardant;
the polylactic acid is selected from one or two of L-polylactic acid and D-polylactic acid.
2. A heat and flame resistant polylactic acid material according to claim 1,
the polylactic acid is a mixture of L-polylactic acid and D-polylactic acid.
3. A heat and flame resistant polylactic acid material according to claim 2,
the mass ratio of the L-polylactic acid to the D-polylactic acid is (0.1-5): 1.
4. A heat and flame resistant polylactic acid material according to claim 1,
the organic hypophosphite flame retardant is selected from one or more of organic hypophosphite halogen-free flame retardants, preferably from one or more of diethyl aluminum hypophosphite, diethyl zinc hypophosphite, ammonium polyphosphate, [ (6-oxo-6H-dibenzo- (c, e) (1,2) -oxaphosphorin-6-one) -methyl ] -succinic acid and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.
5. A heat and flame resistant polylactic acid material according to claim 1,
the mass ratio of the organic hypophosphite flame retardant to the polylactic acid is (0.01-0.5): 1.
6. Heat-resistant flame-retardant polylactic acid material according to one of claims 1 to 5,
the limit oxygen index of the heat-resistant flame-retardant polylactic acid material is 22-27%, the thermal deformation temperature is 160-180 ℃, and the Vicat softening temperature is 145-170 ℃.
7. The preparation method of the heat-resistant flame-retardant polylactic acid material is characterized by comprising the following steps:
step 1, drying the polylactic acid and the organic hypophosphite flame retardant;
and 2, placing the materials dried in the step 1 into an internal mixer for blending.
8. The method according to claim 7, wherein, in step 1,
the mass ratio of the L-polylactic acid to the D-polylactic acid is (0.1-5) to 1;
the mass ratio of the organic hypophosphite flame retardant to the polylactic acid is (0.01-0.5): 1.
9. The production method according to claim 7, wherein, in the step 2,
the blending temperature is 160-220 ℃, and the blending time is 2-10 min.
10. The production method according to claim 7, wherein, in the step 2,
after the blending is finished, isothermal treatment is carried out, the temperature is 160-180 ℃, and the isothermal time is 1-5 min.
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